Methane (CH4) is the second largest contributor to global warming and the importance of reducing net CH4 emissions was recently highlighted through the 2021 Global Methane Pledge. Upland forest soils are most often acting as CH4 sinks, but forest management – for example clear cutting and nitrogen (N) fertilization – carry the potential to turn CH4 sinks into CH4 sources. However, little is currently known about the underlying mechanisms and to what extent forest management affects the fluxes. Furthermore, the role of deadwood in the CH4 cycle is poorly understood and quantified but has recently received increased attention. Deadwood, like soils, can act both as a sink and a source of CH4 and the few available studies indicate that tree species, decay class and wood density are important regulators of CH4 cycling in deadwood.

In the ForBioFunCtioN-project, we utilize state-of-the-art technology (LI-7810 Trace Gas Analyzer, LI-COR®) for in situ measurements of soil-atmosphere and deadwood-atmosphere exchange of CO2 and CH4 in an extensive climate and management manipulation experiment. Treatments include warming with open-top chambers, increased precipitation (on average 25 mm/year during the snow-free period), N fertilization (NH4NO3 150 kg/ha) and biochar addition (10 t/ha) in a total of 12 treatment combinations (n = 144) across five Norwegian spruce dominated bilberry forest sites spanning from a recent clear-cut to mature managed (80 years) and old unmanaged (140 years) stands.

Here, we present the experimental setup of ForBioFunCtioN and soil and deadwood CH4 flux measurements from the snow-free period in 2021 and 2022. Initial results showed that N fertilization decreased net soil CH4 consumption and that, while at rare occasions functioning as a sink, the Norwegian spruce deadwood was almost exclusively a source of CH4. The source strength of deadwood differed substantially between sites but CH4 efflux from deadwood increased by biochar addition at all sites.